1. Field of the Invention
This invention relates to a position detecting apparatus for a moving body, and particularly to a position detecting apparatus for a moving body which is made compact as a whole and yet designed to highly accurately detect the relative positional information of slit means provided with respect to a moving body moving relative to a detecting unit body having light projecting means and light receiving means.
2. Related Background Art
A so-called photoreflector, a photointerrupter or the like is known as a detecting apparatus designed to photoelectrically read a predetermined pattern provided with respect to a moving body by the use of light projecting means and light receiving means to thereby detect positional information such as the amount of movement of the moving body.
Also, measuring instruments which can accomplish the measurement of one submicron or less by the utilization of the interference of laser light are proposed, for example, by Japanese Laid-Open Patent Application No. 59-187203, Japanese Laid-Open Patent Application No. 60-93311 and Japanese Laid-Open Patent Application No. 60-93312. Among these, the measuring instrument utilizing a laser is relatively bulky and therefore is used in a large apparatus.
On the other hand, a detecting apparatus such as a photoreflector or a photointerrupter is relatively small and therefore is incorporated for use for example, in a small space in a lens barrel or the like.
Also, each of these detecting apparatuses detects the repetition signal of a light signal and a dark signal based on the movement of a pattern of predetermined pitch provided with respect to a moving body by the use of light projecting means and light receiving means to thereby detect the amount of movement of the moving body. For example, by the use of a position detecting sensor such as a PSD (position sensitive device), the amount of movement of a slit formed on the detection surface thereof is measured to thereby detect the positional information of the moving member.
FIG. 4 of the accompanying drawings is a schematic view of the essential portions of a conventional position detecting apparatus of this kind.
In FIG. 4, the reference numeral 11 designates a light projecting element which is, for example, an iRED (infrared light emitting diode). The reference numeral 12 denotes a light receiving element such as a PSD. The light receiving element 12 has a light receiving surface 12a of a predetermined length. The reference numeral 13 designates a moving body on the surface of which is provided with a slit 13a.
The image of the slit 13a is projected onto the light receiving surface 12a of the PSD 12 by a light beam from the light projecting element 11. As the moving body 13 moves in the direction of arrow 14 at this time, the image of the slit 13a projected onto the light receiving surface 12a also moves. The PSD 12 is such that, in conformity with the position of the slit image projected onto the surface thereof, the output ratio from an electrode A and an electrode B varies and therefore, by the amount of variation at this time being measured, positional information such as the amount of movement of the moving body 13 is detected.
In the position detecting apparatus shown in FIG. 4, if a plurality of slits are appropriately provided in the moving body 13, an amount of movement greater than the length of the light receiving surface 12a in the direction of detection can be detected.
The detection accuracy of the positional information of the moving body 13 in the position detecting apparatus shown in FIG. 4 depends on the detection accuracy of the light receiving element 12, that is, depends on the detection resolving power as to how finely the positional information of the slit image projected onto the light receiving surface 12a of the light receiving element 12 is resolved and detected.
As regards the PSD used in the position detecting apparatus shown in FIG. 4, it is generally necessary to design the light receiving surface thereof so as to have a predetermined or larger size, but if the light receiving surface becomes large, the detection resolving power will be reduced in many cases.
This has led to the problem that where the detection of the positional information of a moving body is to be effected by the apparatus shown in FIG. 4 and by the use of a light receiving element such as a PSD of a predetermined size, the positional information cannot be detected at an accuracy higher than the detection resolving power of the light receiving element.